Since various items of data are required for controlling motor vehicles, it has been proposed to provide a sensor on a hub unit comprising a wheel-side raceway member to which a wheel is to be attached, a body-side raceway member to be fixed to the vehicle body, and two rows of rolling bodies arranged between the two raceway members.
For example, the publication of JP-A No. 1991-209016 discloses a sensor-equipped hub unit wherein an annular support member is attached to the inner end face of a body-side raceway member and provided with a stain sensor.
The control means recently in use for motor vehicles include drive force control means not permitting pinning of the drive wheels when the vehicle is started or accelerated, and braking force control means for suppressing lateral skidding for cornering, in addition to the ABS control means (antilock brake system). To ensure more accurate control, it has become important to detect data which is usable effectively for these modes of control.
In view of the above situation, the present inventor has conceived the idea of improving the control of vehicles by accurately measuring the ground contact load acting on the tire (wheel).
However, since the conventional hub unit having a sensor is adapted to measure the stain of the annular support member, the ground contact load determined from the strain involves a great error, so that the hub unit has the problem that the ground contact load can not be obtained with high accuracy from the measurement of the strain sensor.
An object of the present invention is to provide a hub unit having a sensor and adapted to determine ground contact loads with high accuracy.